The present invention relates to the field of power over Ethernet and more particularly to a power over Ethernet system exhibiting a dynamic guard band preventing powering of additional ports.
The growth of local and wide area networks based on Ethernet technology has been an important driver for cabling offices and homes with structured cabling systems having multiple twisted wire pairs. The ubiquitous local area network, and the equipment which operates thereon, has led to a situation where there is often a need to attach a network operated device for which power is to be advantageously supplied by the network over the network wiring. Supplying power over the network wiring has many advantages including, but not limited to: reduced cost of installation; centralized power and power back-up; and centralized security and management.
Several patents addressed to this issue exist including: U.S. Pat. No. 6,473,608 issued to Lehr et al., whose contents are incorporated herein by reference, and U.S. Pat. No. 6,643,566 issued to Lehr et al., whose contents are incorporated herein by reference. Furthermore a standard addressed to the issue of powering remote devices over an Ethernet based network has been published as IEEE 802.3af-2003, whose contents are incorporated herein by reference, and is referred to hereinafter as the “af” standard. A device receiving power over the network wiring is referred to as a powered device (PD) and the powering equipment delivering power into the network wiring for use by the PD is referred to as a power sourcing equipment (PSE).
Commercially available PSEs are supplied supporting a single port, or supporting a plurality of ports. For clarity, each port of a power over Ethernet (PoE) controller serving a plurality of ports is referred to as a PSE and exhibits electrical characteristics as described in the “af” standard.
A PoE controller serving a plurality of ports preferably is provided with a power management functionality which prevents powering of ports when the total power consumption of all ports drawing power is within a predetermined range of the available overall power. In an exemplary embodiment this is accomplished by providing a guard band as described in copending U.S. patent application Ser. No. 10/949,208 filed Sep. 27, 2004 entitled “METHOD AND APPARATUS FOR POWER MANAGEMENT IN A LOCAL AREA NETWORK”, published as US 2005/0049758 A1, the entire contents of which is incorporated herein by reference. In an exemplary embodiment the guard band is equal to, or greater than, the maximum power which may be drawn by a port, or PD, disregarding the effect of inrush current. Thus, by implementing the guard band, no PD can be powered which would bring the total utilized power to be in excess of the total available power. It is to be understood that in the event the total utilized power is in excess of the total available power, unless power to at least one port is disabled, the power supply will overload and shut down.
The power management function further operates to monitor the total power consumption of the system. In the event that power consumption is within the guard band limit of the total available power, no additional PDs are powered. In the event that power consumption meets or exceed the total available power, or alternatively meets or exceeds a limit set below the total available power, PDs are disabled to reduce total power consumption. Preferably, PDs are disabled while maintaining priority, thus low priority PDs are disabled first, while higher priority PDs are powered.
Each PD is connected to a unique port of a particular power over Ethernet controller, and thus disabling the port is synonymous with disabling the PD.
The above mechanism is generally satisfactory, however in the event a small power supply is utilized, having a capacity on the order of 2-4 fully powered “af” ports, the guard band prevents utilization of a significant portion of the power supply capabilities. This is particularly problematic in the event that the attached PDs draw power well below the maximum allowed by the “af” standard, and thus a significant number of PDs could be powered in the absence of the above mentioned guard band.
What is needed, and not supplied by the prior art, is a method of dynamically providing a guard band which enables a maximal number of PDs to be powered without exceeding the capabilities of the power supply.